A Note on Transneuronal Atrophy in the Human Lateral Geniculate Body

Abstract

The phenomenon of atrophy in nerve cells after loss of their afferent connexions has been known for many years, but has been demonstrated unequivocally only in the lateral geniculate body, where it results from the degeneration and loss of afferents from the retina. It is shown by a diminution in the size of the perikaryon of the neurones, a somewhat variable loss of Nissl granules, a loss of intercellular neuropil (due to degeneration of fibres from the retina), and glial proliferation. Although often described in the older literature as a chromatolytic degeneration (e.g., by Minkowski, 1920), it does not present the classical picture of chromatolysis and the usual description as an atrophy of the cells is the more appropriate.Transneuronal atrophy has been described in situations other than the lateral geniculate body, e.g., in the spinal cord of the monkey and man after posterior root section by Foerster, Gagel, and Sheehan (1934) but recent investigations (Cook, Walker, and Barr, 1951, and others) have failed to confirm these findings. An atrophy of cells scattered among many which were unaffected would be difficult to detect; this may well be the situation in the spinal cord and may account for the lack of confirmation. The lateral geniculate body, where all the cells receive their afferents predominantly and p_rhaps exclusively from the retina, might well show the process in its most obvious and easily detected form, and is clearly the region most suitable for its study.There is much evidence to show that transneuronal atrophy in the lateral geniculate body differs in the rate at which it proceeds and probably also in the degree it reaches in different mammals. With the exception, however, of the work of Cook et al. (1951) in the cat and rabbit, it is difficult to make comparisons from the published accounts since quantitative methods have not been used to describe the degree of atrophy. It seems certain that the process is rapid and fulminating in primates, for changes are evident within seven days of section of the optic nerve (Glees and Clark, 1941). In the cat Cook et al. found that changes first became noticeable in the second month, and in the rabbit that they were even slower in their development. In the cat the atrophy amounted to about 25 % of the cross-sectional area of the cell, and did not increase up to 10 months after deafferentation (Cook et al., 1951).The normal primate lateral geniculate body, including that of man, has been studied extensively by quantitative methods (Balado and Franke, 1937;Chacko, 1948 and 1949) so that information about normal cell size, the total number of cells and their density is fairly complete. There appear, however, to be no similar studies of the cells in transneuronal atrophy, so that when a human specimen became available it seemed desirable that it should be investigated quantitatively. The primate lateral geniculate body is particularly suitabie for this purpose since, owing to its laminar structure, normal and atrophic laminae are available side by side...

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